BTU to kW Calculator

How the BTU/hr to kilowatt conversion works

BTU per hour (BTU/hr) and kilowatts (kW) both measure the rate at which energy is transferred — power. They are linked by a fixed thermodynamic relationship: 1 kilowatt equals exactly 3,412.142 BTU/hr. To convert BTU/hr to kW, divide by that factor: kW = BTU/hr ÷ 3,412.142. The result is exact for the rate entered; no estimation or approximation is involved in the arithmetic.

The exact conversion factor and its origin

One BTU (British Thermal Unit) is the amount of heat required to raise one pound of water by 1 °F at standard conditions. One kilowatt-hour is 3,600,000 joules (3,600 kJ). Converting BTU to joules: 1 BTU = 1,055.05585 J (the IT definition used in ASHRAE and most HVAC standards). Multiply: 3,600,000 J/hr ÷ 1,055.05585 J/BTU = 3,412.142 BTU/hr per kW. This is the ASHRAE/AHRI-standard factor used for rating heating and cooling equipment.

The calculator uses 3,412.142 BTU/hr = 1 kW, giving: kW = BTU/hr ÷ 3,412.142. Results are displayed to three decimal places.

What a ton of refrigeration is

In US HVAC practice, air-conditioning capacity is expressed in tons of refrigeration as well as BTU/hr. One ton of refrigeration is defined as 12,000 BTU/hr — the rate of heat absorption required to melt one short ton (2,000 lb) of ice in 24 hours. Converting: 12,000 BTU/hr ÷ 3,412.142 = 3.517 kW per ton. The calculator shows this alongside kW so an equipment rating given in tons reads directly as a kilowatt figure without a second lookup.

Outputs shown by this calculator

kW (kilowatts): the primary SI power unit for electrical load calculations and international equipment specs. Tons of refrigeration: the US industry standard for air-conditioning capacity (1 ton = 12,000 BTU/hr = 3.517 kW). Watts: kW × 1,000 — the same value in the base SI unit, useful for comparing against electrical panel ratings or circuit breakers. Mechanical horsepower: kW × 1.34102 — the traditional unit sometimes seen on older equipment nameplates (1 mechanical hp = 745.7 W = 2,544.43 BTU/hr).

Worked examples (verified)

A 1-ton window air conditioner: 12,000 BTU/hr ÷ 3,412.142 = 3.517 kW (1.000 ton, 3,517 W, 4.716 hp). A 2-ton central unit: 24,000 BTU/hr ÷ 3,412.142 = 7.034 kW (2.000 tons, 7,034 W, 9.432 hp). A 3-ton system: 36,000 BTU/hr ÷ 3,412.142 = 10.551 kW (3.000 tons, 10,551 W, 14.149 hp). A 4-ton system: 48,000 BTU/hr ÷ 3,412.142 = 14.067 kW (4.000 tons, 14,067 W, 18.865 hp). A 5-ton system: 60,000 BTU/hr ÷ 3,412.142 = 17.584 kW (5.000 tons, 17,584 W, 23.581 hp).

Where BTU/hr and kW appear in US HVAC practice

US residential and light-commercial HVAC equipment — air conditioners, heat pumps, furnaces, boilers, water heaters — is rated in BTU/hr or in tons of refrigeration (cooling only). Electrical engineers and utility engineers work in kilowatts when sizing service panels, calculating demand loads, or comparing a heat pump against its electrical draw. International equipment catalogs, ISO and EN standards, and European or Canadian specification sheets express ratings in kW. Converting between the two is a routine step when specifying equipment across those boundaries.

ASHRAE Standard 90.1 (Energy Standard for Buildings) and IECC energy code compliance calculations reference efficiency metrics such as COP (coefficient of performance), EER (energy efficiency ratio), and SEER (seasonal energy efficiency ratio), all of which involve the ratio of BTU/hr output to watt input. This calculator produces the kW figure that feeds those ratios.

The room volume calculator determines a space's heating or cooling load in BTU/hr (via a Manual J or rule-of-thumb method); the BTU-to-kW conversion then translates that load into the kW figure needed for heat-pump or mini-split selection sheets, which often list both units side by side.

Precision and rounding

The calculator displays kW and tons to three decimal places, watts to the nearest whole number, and horsepower to three decimal places. The underlying factor 3,412.142 is rounded from the more precise 3,412.14163... BTU/hr — the same rounding used in ASHRAE and AHRI publications. For equipment sizing, three decimal places in kW represents precision well below any measurement uncertainty in the load calculation; the conversion itself is not the limiting factor.

Using this alongside other BuildMetricLab tools

The Fahrenheit-to-Celsius calculator handles temperature-unit conversion for HVAC performance data that states outdoor design temperatures in °F while equipment curves are drawn in °C. The room volume calculator provides the cubic footage needed for rough BTU/hr load estimation. The towel warmer BTU calculator converts small radiant-heat appliance ratings. All BuildMetricLab tools run entirely in the browser — no sign-up, no data sent anywhere, and every formula is shown on the page so the math can be audited.